This application claims the priority of European patent document 00110423.1, filed May 16, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an occupant-restraining system which limits the restraining force exerted on an occupant via a restraining belt.
Safety restraining systems are found today on most seats in motor vehicles. When the vehicle is involved in an accident, they are used to keep the injuries to the occupants as slight as possible. Use is made these days, inter alia, of active systems, such as, in particular, seat belts and what are referred to as xe2x80x9cair bagsxe2x80x9d.
An air bag generally known in practice is a gas sack which can be inflated automatically in the event of an accident, and which, when not in use, is folded in an accommodating space, for example below the windshield, laterally in the seat, in the door, or else in the footwell of the vehicle. At a critical driving state, the gas sack is inflated so that it emerges from this accommodating space. Inflation takes place within a short period, by means of a sensor-controlled gas generator, with the result that a balloon-like protective cushion is formed to protect the occupant.
In addition, seat belts have long been used in motor vehicles to protect the occupants. Many different types of seat belts are therefore also known. Thus, many vehicles are, for example, equipped with belts which are commercially available and are arranged at either two or three fastening points in the vehicle. They are intended to prevent the force of inertia due to a sudden, sharp braking or impact of the vehicle against an obstacle from causing the bodies of the people in the vehicle to be flung forward.
If a vehicle collides against an obstacle, in particular at high speed, the force of inertia causes the occupants to be hurled forward. If safety devices are not present, accidents of this type generally end with the people in the vehicle having severe and sometimes fatal injuries. If, in contrast, the vehicles are equipped, inter alia, with seat belts, although the occupants generally have prospects of surviving, the restraining force applied by the belt is, under some circumstances, very high for the occupants.
A method for limiting the restraining force exerted on the occupant via a belt in an occupant-restraining system is described, for example, in European Patent Document EP 0 734 922. In this case, the restraining system has a seat belt and inflatable restraining element. The restraining force exerted on the occupant by the belt is limited by a force limiter to a level which can be set, and can be adjusted to the body size or the weight of the vehicle occupant. The level of force is set here in such a manner that in the characteristic curve depicting the force over the path of forward displacement within a section after the transition of which the contact between the belt band and inflated restraining element is anticipated, the characteristic curve has a tapering-away tendency. The force limiter itself is designed in such a manner that the restraining force is limited by plastic deformation of material and the severity of the deformation of the material is variable, depending on parameters which are representative of the body size or the weight of the occupant.
This technique for limiting force, however, has proven disadvantageous in that the severity of the accident does not have any effect on the limitation of force; therefore in all types of accidents, irrespective of their severity, the restraining force exerted on the occupant is limited, which is not always desirable.
German patent document DE 196 04 483 C1 discloses a safety device for motor vehicles, in which a control device connected to measuring sensors is provided for controlling the restraining characteristics of the safety device, which has a seat belt, for the occupant in the vehicle within the bounds of the range of human endurance. The safety device is intended to be set up for the best possible restraining characteristic. For this purpose, the control device is coupled to a blocking device for the belt band (which blocking device has a force-limiting device permitting a limited extension of the belt band), in such manner that the force profile originating from the force-limiting device and/or the amount of permissible extension of the belt band (up to complete blocking of the extension of the belt) is monitored, controlled and limited as a function of the occupant""s body data detected by the control device, the seat-position data relating to the passenger cell and/or the data concerned with the accident conditions.
This safety device, has the disadvantage that the influence of other safety restraining devices in the vehicle is not taken into consideration. Also, no consideration is given to the effect of the variables concerned with occupant position, body data of the occupant and data concerned with the accident conditions have on the level of force or on the limitation of force.
One structural implementation of a force limiter is described in German patent document DE 43 31 027 C2, in which a self-locking seat-belt retractor has a blocking arrangement that can be activated in a vehicle-sensitive and/or belt-band-sensitive manner. A tensioning arrangement which acts on the belt-winding-up shaft and is provided with a drive arrangement, in which the belt retractor is provided with a force-limiting device for a limited extension of the belt band. The intention is to ensure that during normal operation of the seat-belt retractor, the force-limiting device is not subject to any stress. For this purpose, it is provided that the force-limiting device can be switched on and off via an interconnected coupling as a function of the functional states of the belt retractor and/or of the tensioning arrangement.
Even in this belt-force limiter no criteria are specified for the type of limiting of the belt force. In addition, other occupant-restraining devices likewise have no effect on the level of force exerted in the case of this belt-force limiter.
One object of the present invention is to provide an occupant-restraining system which limits the restraining force exerted on an occupant via a belt, and further reduces to a minimum the loads on the occupant in the event of an accident, while at the same time also of setting the restraining force to a required extent.
This and other objects and advantages are achieved by the occupant restraining system according to the invention in which the force exerted on occupants via a restraining belt can be switched (depending on an inflating time of an air bag, the occupant""s weight, a crash level and a forward displacement of the occupant) from a relatively higher to a relatively lower level of restraining force, when a belt-force limiter is activated.
Because the belt-force limiter is activated only after a predetermined forward displacement of the occupant, limitation of the belt force is activated only when a relatively great forward displacement of the occupant has actually taken place.
Because the belt-force limiter is also activated only after an inflation time of the air bag, it is thus possible, in an early accident phase, for the occupant to be coupled to the vehicle with great belt-restraining force, while at a later time in the sequence of movement, the air bag (which has been filled in the meantime) shares this task. However, it is necessary for this purpose that the occupant has anyway reached a predetermined forward displacement, and that the air bag is also completely inflated. As a result, an excessive increase of forces on the occupant can be avoided.
Furthermore, it is important that the belt-force limiter is not activated if the accident or crash intensity is too severe and/or if the occupant""s weight is too great. In such a case, the belt also has to take on the restraining function, since optimum securing of the occupant cannot otherwise be ensured. That is, the occupant must always to be held back, despite having already been displaced forward and despite the air bag having been triggered on account of the great weight and/or severity of the accident.
In this case, it would even be conceivable that in the case of a very severe accident and/or a very great occupant""s weight the restraining force is not only not limited, but under some circumstances is even increased.
In order, therefore, to avoid an excessive increase of forces in the case of an accident, the belt force is switched back when the weight of the occupant and/or the severity of the accident are not too great, and such switching back is not disadvantageous. In this manner, excessive increases of forces on the occupant can be avoided, so that less severe accidents, in particular, result in fewer undesirable adverse effects for the occupant.
It should be taken into consideration that the term accident or crash is not always to be understood here as meaning that the vehicle is actually involved in an accident; rather, the term xe2x80x9caccidentxe2x80x9d is also to be understood as all other critical driving states, such as, for example, even very severe braking or skidding.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.